Fluorescent tube with mercury amalgam on tube wall



July 26, 1966 u. w. DOERING 3,263,111

FLUORESCENT TUBE WITH MERCURY AMALGAM ON TUBE WALL Filed Aug. 2. 1952 United States Patent O 3,263,1i1 FLURESCENT TUBE VVHTH MERCURY AMALGAM N TUEE WALL Ulrich W. Deering, Ainmillerstr. 37, Munich I3, Germany Filed Aug. 2, 1962, Ser. No. 214,431 lll Claims. (Cl. 313-109) The invention relates to a highly loaded fluorescent lamp with a filling of rare gas and an addition of mercury vapor, preferably with activated hot electrodes and a coating of fluorescent materials on the interior wall of the elongated, tube-like discharge vessel, in which the rise of the mercury vapor over the saturation pressure of the pure mercury corresponding to a temperature of 40 to 50, i.e. over about 0.01 mm. Hg is prevented by using the mercury in the form of an amalgam. The amalgam is afiixed preferably to the wall of the tube, as proposed before by the inventor, for example, in the form of a small sheet, e.g. such of 1/s-l mm. thickness and l cm.2 area.

It has been also proposed, when making the lamp, to remove in a certain confined space the fluorescent material uniformly coating the tube-like vessel, and to deposit the amalgam there. To ydo this is complicated and, in the case of afllxing the amalgam in the midst of the tube it is not easy to accomplish.

According to the invention, when making the tube, an area or a spot of solid and firm surface property will be generated within the range of the fluorescent coating which loosely covers the inner surface of the vessel, on which area the amalgam body will be deposited and therefore stick to it. This area or spot has a permanent or transient overlay or covering of suitable substances which are able, either to repel the liquid, in which the fluorescent materials are suspended, and to preserve clean the surface of the tube wall in this area lor which are able to solidify the loose fluorescent coating at this confined space, and therefore in either case to make the amalgam stick to this spot.

The invention may be explained more in detail by referring to the figures, which however are only possible embodiments.

All the figures are cross-sectional views of a portion of an elongated fluorescent tube containing the amalgam deposit. FIG. 4 represents a cross-section of a complete end portion of the tube showing one of the electrodes.

FIGS. 1 4 show successive steps in realizing the invention when making the lamp.

FIGS. 5-6 represent two significant stages in the production of the lamp according to Vanother embodiment of the invention, and FIG. 7 shows still another embodiment of a portion of a completed tube.

In FIG. l reference character 1 represents in a longitudinal sectional view a part of `the body of the tube preferably of usual dimensions, e.g. of 38 mm, diameter and 80-150 cm. length. Before coating the tube with fluorescent material, a substance, which repels the liquid, in which the fluorescent materials are suspended, is deposited on the interior surface of the wall in the form of an over lay or covering 2 on a confined small spot corresponding in size to the later amalgam deposit.

FIG' 2 shows the tube after depositing the suspended fluorescent material, which forms an all around interior coating 3 on the tube wall, whereas the repelling overlay 2 is free of it. Suitable substances for this purpose are such of the type of the polyvinyls, polynitriles and, even more strongly repelling, such on the basis of silicone. They may be deposited in a molten state or dissolved in a solvent. Furthermore they have the property that they will evaporate or disintegrate when heated without form- ICC ing a residue, so that an area free of the fluorescent coating and exposing the firm and clean glass Wall will be formed. Also numerous nitrous compounds will be suitable for this purpose. It is advantageous to add substances sucn as boric acid or easily melting fluorides in order to etch and roughen the glass .surface and t-o make it more sticky for the amalgam.

FIG. 3 shows the tube after the usual firing of the fluorescent materials by which they are burnt to the glass wall forming an all round loose coating on it, whereas at the place of the overlay 2 the glass wall is free of these fluorescent materials.

FIG. 4 shows one end portion of a completed tube, in which e.g. at a distance of only 8-12 cm. from the ends a spread out or disc-like amalgam mass 4 is deposited finally on the free glass wall area created as mentioned before.

According to FIG. 5, easily melting or sintering inorganic substances may be deposited as an overlay or covering S at least at one confined place of the interior tube wall which is not yet coated with the fluorescent materials. The substances will sinter together with the fluorescent materials 3, after the latter have been deposited in the usual manner and the tube will be fired Suitable substances are easily melting enamels, boric acid, fluorides, lead compounds especially lead oxide, or easily melting mixtures thereof. They will be preferably deposited as powder, however, together with a binder, e.g. molten together with the latter or suspended in it. It is advantageous to add grainy or coarsely powdered materials such as glass powder, which preferably must not melt during the firing process. Due to the rough surface generated thereby, the amalgam body will stick reliably to this confined space. The tube thereafter will be coated in the usual way with fluorescent materials, which will line the whole tube as shown at 3 in FIG. 6 and even may cover the overlay 5. If water is used as the suspending liquid for the fluorescent materials, it is recommended to use an inorganic binder or solvent for the repelling sintering substances not soluble in Water. In case the fluorescent materials will be used together with an inorganic liquid, reversely, binders or solvents not soluble in the latter liquid must be used.

When firing the tube the overlay 5 according to` FIGS. 5 and 6 Will sinter firmly to the glass Wall, and it will also sinter together with the fluorescent materials, at least it will consolidate and solidify the latter so far that it becomes sufliciently solid 'and will stick rmly to the glass wall, so that the disc of amalgam deposited later on will stick reliably in turn to it and will not scale oli the Wall together with the fluorescent materials.

The methods may also be combined by mixing the melting for sintering substances according to FIGS. 5 and 6 with means according to FIGS. 1-4, which repel the suspending liquid, or by impregnating the former 'with the latter or by suspending the former in the latter.

A further method consists in depositing the substances mentioned above in the form of a limited spot 7 in FIG. 7 on the interior wall of the tube already coated with the fluorescent materials 3, however not yet tired. The easily melting or sintering substances in this case will sinter together with the underlying fluorescent material, will penetrate it and will sinter additionally to the glass wall 6, so that the amalgam body 4 deposited later on, will stick firmly and securely.

The amalgam may be spread in a liquid state on the spot, which is free of fluorescent materials or which is covered with sintered and sufficiently solid material or with fluorescent material sufliciently solidified and sintered to the wall as described above, e.g. it may be dribbled on the spot mentioned. Instead of this, a prepared small sheet or disc or a foil of amalgam may be pressed on the prepared spot and advantageously afllxed by heating. Lamrnae or discs of 1/s to 1 or 2 mm. thick-according to the mercury content of the amalgam-and of 1/2 to a few cm.2 area will be suflicient for tubes of usual size.

The amalgam may be placed as known in the art on the coldest spot i.e. in the midst of the tube. However, contrary to the common opinion the amalgam need not be provided at the coldest place of the tube, but can be deposited at considerably warmer portions of it, for example at one or two spots 8-12 cm. distant from the one or two ends of the tubes respectively. Advantageously the spots should not be chosen in the immediate proximity of the electrodes, however in a range, where Ythe temperaturehasdropped to7080 C. Now, according to the invention an amalgam with a small content of mercury will be chosen in this case, which is determined so that its vapor pressure at these .temperatures wi'll not exceed about 0.01 mm. Hg.

Notwithstanding the fact, that the middle portions of .the tube are considerably cooler, no migration of mercury thereto will happen. The vapor filling after switching off the tube certainly will condense mostly at the coldest portions and additional evaporation from the more quickly heated amalgam will happen when the lamp is switched on again. However, this will be compensated perpetually by re-absorption of the :mercury by the amalgam body.

An amalgam with small mercury content may be also used for very highly loaded lamps. By this, lamps may be understood, which are loaded 4-5 times the usual load of a 40 w.lamp at the 'same dimensions of .the lamp vessel, or in which even the coldest areas assume temperatures of 70-80 C. and more. With tubes conventional in recent times and sold by some big firms with dimensions of 38 mm. diameter and about 1200 mm. length, this will correspond to loadings of more than 125 w., in general of 150-250 w. Differing from this, under simple highly loaded lamps may be understood such, in which (when suspended in free air and at ambient temperatures of 22-25 C.) the coldest areas will assume temperatures of 56 to 60 C., which will happen at loads up to two and a half as large as the conventional loads, eg. at -about 100 w.

According to an easily adjustable method, metal powder, foils, sheets or discs, suitably, however, Imade of Iamalgam of the metals, will be loaded with mercury by enclosing them in an evacuated container, at temperatures corresponding to their later operating temperature. In the ycontainer or in an annex to it a supply of mercury is provided at the same time under a temperature of about 40 C. or less corresponding to a pressure of not more than 0.01 mm. Hg.

A poor cadmium amalgam containing less than 33 atomic percent mercury has been found suitable for lamps loaded 2-3 times the usual load of a tube 40 w., 38 mm. diameter and 1200 mm. length; a Cd-amalgam of less than 20 atomic percent for lamps loaded 4-5 times the normal; a tin -amalgam of 10 atomic percent Hg content and less for 2-3 times, :and of 5 atomic percent Hg for 4-5 times overloaded lamps. Gold amalgams preferable as foils of less than 14 atomic pe-rcent are suitable in 2-3 times, land of less than 6 atomic percent for 4-5 times overloaded tubes. Likewise are suitable silver arnalgams with Hg contents in the same ranges. Furthermore a potassium amalgam of 25 atomic percent potassium (corresponding to 75% Hg content) in tubes of 2-3 times, and such of 33% K (corresponding 67% Hg) for tubes loaded 4-5 times are appropriate. The tubes assumed in the foregoing as a base for comparison are, however, no physical, but solely commercial standards.

Despite the relatively high melting point of silver such :amalgams will reach the equilibrium state very quickly, as the speed of diffusion of the mercury atoms in it is very high. Similar properties apply for gold amalgams.

As the other amalgams, especially such containing cadmiurn, tin, lead etc. proposed already frequently are rather soft at operating tempe-ratures, the speed of reaching equilibrium is no problem. On the contrary, low melting amalgams or such having a too high vapor pressure may be hardened or lowered with respect to their vapor pressure by adding small amounts of alkaline or alkaline earth metals.

What I claim is:

1. In a fluorescent tube of the character described, in combination, a tube having an inner surface; incandescent electrodes located in said tube; fluorescent material covering at least the major portion of the inner surface of said tube; a rare gas located in said tube; and a body of one amalgam selected from the group consisting of tin amal- Y gam consisting of tin and up to l0 atomic percent of mercury, gold amalgam Yconsisting of gold and up to l4'atomic percent lof mercury, silver amalgam consisting of silver and up to 14 atomic percent of mercu-ry, and potassium amalgam consisting ot' mercury and between 25 and 33 :atomic percent of potassium, adhering to a relatively small portion of said inner surface of ysaid tube spaced from said electrodes, respectively, at a distance of between about 8 and 12 cm., the mercury content of said body of amalgam being such that at `a temperature of up to about C. `the mercury vapor pressure of said amalgam will not exceed about 0.01 mm. Hg.

2. In a fluorescent tube of the cha-racter described, in combination, a tube having an inner surface; incandescent electrodes located in said tube; fluores-cent material covering at least the major portion of the inner surface of said tube; a rare gas located in said tube; and a body of amalgam selected from the group consisting of tin amalgam, gold amalgam, potassium amalgam and silver amalgam adhering to a relatively small portion of said inner surface of said tube spaced from said electrodes, respectively, at a distance of between about 8 and 12 cm., the mercury content of said body of amalgam being such that at a temperature of up to about 80 C. the mercury vapor pressure of said amalgam will not exceed -about 0.01 mm. Hg.

3. A fluorescent tube according to claim 1 wherein said amalgam is an amalgam other than potassium amalgam and contains a relatively small proportion of a metal selected from the group consisting of alkali metals and alkaline earth metals.

4. In a fluorescent tube of the character described, in combination, la tube having an inner surface, incandescent electrodes located in said tube; fluorescent material covering at least the major portion of the inner surface of said tube; a rare gas located in said tube; and a body of tin amalgam consisting of tin and up to 10 atomic percent of mercury adhering to a relatively small portion of said inner surface of said tube spaced from said electrodes, respectively, at a distance of at least 8 cm.

5. In a fluorescent tube of the character described, in combination, a tube having an inner surface; incandescent electrodes located in said tube; fluorescent material covering at least the major portion of the inner surface of said tube; a rare gas located in said tube; and a body of tin amalgam consisting of tin and up to 5 atomic percent of mercury adhering to a relatively small portion of said inner surface of said tube spaced from said electrodes, respectively, at a distance of between about 8 and 12 cm.

6. In a fluorescent tube of the character described, in combination, a tube having an inner surface; incandescent electrodes located in said tube; fluorescent material covering at least the major portion of the inner surface of said tube; a rare gas located 'in said tube; and a body of gold amalgam consisting of gold and :an effective amount but less than 14 atomic percent of rnercu-ry adhering to a relatively `small portion of said inner surface of said tube spaced from said electrodes.

7. In a fluorescent tube of the character described, in combination, a t-ube having an inner surface; incandescent electrodes located in said tube; fluorescent material covering at least the major portion of the inner surface of said tube; 1a rare gas located in said tube; and a body of gold amalgam consisting of gold and an effective amount but less than 6 atomic percent of mercury adhering to a relatively small portion of said inner surface of said tube spaced from said electrodes, respectively, at a distance of at least 5 cm.

8. In a fluorescent tube of .the character described, in combination, la tube having an inner surface; incandescent electrodes located in said tube; uorescent material covering at least the major portion of the inner surface of said tube; a rare gas located in said tube; and a body of potassium amalgam consisting of mercury and between about 25 atomic percent and 33 atomic percent of potassium :adhering to a relatively small portion of said inner surface of said tube spaced from said electrodes.

9. In a uorescent tube of the Icharacter described, in combination, a tube having an inner surface; incandescent electrodes located in said tube; fluorescent material covering at least the major portion of the inner surface of said tube; a rare gas located in said tube; and a body lof silver amalgam consisting of silver and an effective amount but less than 14 atomic percent of mercury adhering to a relatively small portion of said inner surface of said tube spaced from said electrodes.

10. In a fluorescent tube of the character described, in combination, a tube having an inner surface; incandescent electrodes located in said tube; fluorescent material covering at least the major portion of the inner surface of said tube; a rare gas located in said tube; and a body of silver amalgam consisting of silver and an effective amount but less than 6 atomic percent of mercury adhering to a relatively small portion of said inner surface lof sa-id tube spaced from said electrodes, respectively, at a distance of at least 5 cm.

References Cited by the Examiner UNITED STATES PATENTS 2,216,252 10/1940 Randall 313-109 2,255,761 9/1941 Casellini 313-109 2,984,891 5/1961 Creswold 29-25.13 3,007,071 10/1961 Lompe et al 313-178 3,077,022 2/ 1963 Cullis 29-25.13 3,160,778 12/ 1964 Dzie-rgwa et al 313-179 DAVID J. GALVIN, Primary Examiner.

GEORGE WESTBY, Examiner.

R. SEGAL, D. E. SRAGOW, Assistant Examiners. 

1. IN A FLUORESCENT TUBE OF THE CHARACTER DESCRIBED, IN COMBINATION, A TUBE HAVING AN INNER SURFACE; INCANDESCENT ELECTRODES LOCATED IN SAID TUBE; FLUORESCENT MATERIAL COVERING AT LEAST THE MAJOR PORTION OF THE INNER SURFACE OF SAID TUBE; A RARE GAS LOCATED IN SAID TUBE; AND A BODY OF ONE AMALGAM SELECTED FROM THE GROUP CONSISTING OF TIN AMALGAM CONSISTING OF TIN AND UP TO 10 ATOMIC PERCENT OF MERCURY, GOLD AMALGAM CONSISTING OF GOLD AND UP TO 14 ATOMIC PERCENT OF MERCURY, SILVER AMALGAM CONSISTING OF SILVER AND UP TO 14 ATOMIC PERCENT OF MERCURY, AND POTASSIUM AMALGAM CONSISTING OF MERCURY AND BETWEEN 25 AND 33 ATOMIC PERCENT OF POTASSIUM, ADHERING TO A RELATIVELY SMALL PORTION OF SAID INNER SURFACE OF SAID TUBE SPACED FROM SAID ELECTRODES, RESPECTIVELY, AT A DISTANCE OF BETWEEN ABOUT 8 AND 12 CM., THE MERCURY CONTENT OF SAID BODY OF AMALGAM BEING SUCH THAT A TEMPERATURE OF UP TO ABOUT 80* C. THE MERCURY VAPOR PRESSURE OF SAID AMALGAM WILL NOT EXCEED ABOUT 0.01 MM. HG. 